This application pertains to the art of joints and, more particularly, to flexible sealed joints for conduit. The invention is particularly applicable for use in jet engine bleed air duct systems and will be described with reference thereto. However, it will be appreciated that the invention has broader aspects and may be used in any conduit system wherein limited flexing of sealed joints is desirable for relieving high thermal and structural stresses by deflecting under low bend loads.
It is conventional on jet aircraft to bleed air from the engine compressors for such purposes as aircraft air conditioning, heating, pressurization and anti-icing. The ducting for such bleed air is subjected to a wide range of temperatures and high bend loads are imposed on duct joints as a result of thermal expansion and/or movement, particularly in the ducting takeoff from the bleed pad to common manifolds or other equipment. In order to withstand the high bend loads, stronger manifolds and joints have been used. However, this simply stiffens the ducting at the joints and bend loads become even greater.
Flexible joints have been used for deflecting under the bend loads and such flexible joints have been made using metal bellows. Flexible metal bellows are subject to fatigue failure and are not highly reliable. Another flexible sealed joint is described in U.S. Pat. No. 3,995,896 issued Dec. 7, 1976, to Decker. In the arrangement of the Decker patent, a sealing ring of low friction material, such as carbon, engages one surface of a spherical portion on an internal conduit. A gimbal arrangement is required for pivotally connecting the inner conduit to an outer conduit. The single continuous sealing ring of carbon is also subject to breakage when the parts expand and this could result in seal failure or considerable leakage.
It would be desirable to have a reliable pneumatic joint which was capable of taking the necessary deflections in ducting of the type described. It would further be desirable to have such a joint which could withstand a jet engine environment with an increased life expectancy, as compared to a metal bellows, and yet could be easily refurbished. It would also be desirable to have such a joint which would not require the use of a gimbal arrangement for pivotally connecting inner and outer conduit parts.